The issue occurs on both untouched settings, and with patches and custom settings applied, and on DX9, DX11 and OpenGL.
The patches I use are listed on https://wiki.pcsx2.net/Klonoa_2:_Lunatea%27s_Veil. I do want to note only one of all patches listed on the site (in this case the first listed 2F56CBC9.pnach, which applies to work around a hang in Volk City, a place I haven't been able to visit yet.

Please tell me if I need to provide any more debugging info. Thank you in advance.

I've been doing further investigation and according to this thread, patch 2F56CBC9 should be solving this door crash issue. It seems like the patch is no longer working.
I'm clueless as to what I am supposed to do to have the workaround working, or the other patches aside from 2F56CBC9.

As this post suggests, I'm gonna want to use an older development version of PCSX2, preferably 2175. However, the development releases list and the Windows builds do not show anything older than three or four weeks old. Does anyone have this build available somewhere?